Since Vladimir Putin and Mr Poroshenko last met on June 6 in France, Ukraine has turned the tide of the conflict and largely encircled pro-Russian rebels holding out in two cities in the east of the former Soviet republic.

But the diplomatic crisis has only deepened, especially since the downing of Malaysia Airlines flight MH17 over rebel-held territory last month with the loss of 298 lives.

Stung by US and EU sanctions against its finance, oil and defence sectors, it has hit back by banning most Western food imports in a trade war that is hurting both the Russian and European economies.

Tuesday's talks in the Belarusian capital of Minsk will include European Union foreign policy chief Catherine Ashton and the leaders of Belarus and Kazakhstan, partners in a Russian-led customs union.

But expectations on all sides appear low, with German chancellor Angela Merkel among those playing down any likelihood of a breakthrough to end the fighting in which more than 2,000 people have been killed since April.